Removal and Survival of Fecal Indicators in a Constructed Wetland after UASB Pre-Treatment

Fabio Conti,Massimo Raboni,Elena Cristina Rada,Paolo Viotti

doi:10.3390/su13169302

Abstract

The experimentation plant, based on a sub-surface horizontal flow phytodepuration (SSHFP) unit with a pre-treatment by an upflow anaerobic sludge blanket (UASB) reactor, proved valuable in treating the sewage of a small rural community located in north Brazil. During a six-month trial, the plant achieved an average removal efficiency of 98.2% (1.74 log removal) for fecal coliforms (FC) and 96.0% (1.40 log removal) for Enterococci (EN), as well as 95.6% for BOD5, 91.0% for COD,00 and 95.4% for suspended solids (SS). The contribution of the UASB reactor to this overall performance was very significant as, alone, it achieved a yield of 62.7% for FC and 60% for EN, in addition to 65.2% for BOD5 and 65.0% for SS. EN was chosen, in addition to FC, because of its higher specificity and strong environmental persistence, leading to an increased risk to human health. In fact, the experimental results confirmed its lower removal efficiency compared to FC. The mechanical and biological mechanisms that led to such a removal efficiency of the two fecal indicators (FIs) are outlined in the article. The same mechanisms led to a good level of equivalence between the removal efficiency of the two FIs with the removal efficiency of SS and BOD5, for both the whole plant and the UASB reactor alone. The research demonstrated the close correlation between the concentrations of EN and FC for the plant effluent. This correlation can be explained by the following mathematical expression of the regression line Log EN = 0.2571 Log FC + 3.5301, with a coefficient of determination R2 = 0.912. This implies that the concentration of the more specific indicator EN could be calculated, with acceptable approximation, from the simple analysis of FC and vice versa. The experimental plant brought important health benefits to the local population. In particular, there were no significant odor emissions; moreover, the risk of fecal pathogenic diseases was drastically reduced; finally, there was no proliferation of insects and other disease vectors, due to the absence of stagnant or semi-stagnant water exposed to the atmosphere.

Highlights

This means that the homogeneity and quality of the final effluent allows researchers to calculate, with good reliability, the concentration of the more specific indicator EN from the simple analysis of fecal coliforms (FC) and vice versa
The investigated plant, based on a upflow anaerobic sludge blanket (UASB) reactor followed by a sub-surface horizontal flow phytodepuration (SSHFP) system, proved valuable for the treatment of sewage in a small rural community of 1650 inhabitants
The contribution of the UASB reactor to this overall performance proved to be very significant as it alone achieved a 62.7% yield for FC and 60.0% for EN, as well as 65.2% for BOD5 and 65.0% for SS

Summary

Introduction

Sewage is the main cause of fecal contamination of water bodies and, as such, it constitutes a serious health risk due to pathogenic microorganisms excreted by infected people. These infectious vectors belong to the huge kingdoms of bacteria, protozoa, and viruses. Helminths, which, in effect, are pluricellular parasitic worms, are often associated with the microorganisms’ microcosm because of their microscopic eggs and larvae that cause diseases. Helminths, which, in effect, are pluricellular parasitic worms, are often associated with the microorganisms’ microcosm because of their microscopic eggs and larvae that cause diseases. 4.0/).

Methods

Results

Conclusion